1. Field of the Invention
This invention relates generally to creating fractional treatment using a patterned cooling spray and an optical source, for example by using a patterned cryogen spray with a laser source to create a pattern of microscopic treatment zones for cosmetic dermatological treatment.
2. Description of the Related Art
Light sources (e.g., lasers, LEDs, flashlamps, etc., including in the non-visible wavelengths such as infrared) are frequently used to treat biological tissues inside and outside the human body through a photothermal process that comprises heating the tissue using light absorbed by the tissue. In this photothermal process, a target tissue or its constituents absorb the treatment light and convert the light energy into thermal energy to cause thermal damage or stimulation to the tissue.
If photothermal treatment uses a wide beam of light, particularly with a wavelength that is non-selective, such as a wavelength primarily absorbed within the tissue by water, it can be difficult to optimize the parameters to achieve treatment that is both effective and has a low risk of side effects. If the delivered optical fluence is too high, the region can be overtreated, resulting in slow healing and other side effects. If the delivered optical fluence is too low, the stimulation may be too weak to cause the desired treatment. Thus, broad area photothermal treatment is limited in the levels of treatment that are simultaneously effective and safe.
Fractional photothermolysis addresses this limitation of broad area photothermolysis by using a patterned distribution of light to irradiate only a fraction of the tissue with high intensity light. Thus, in fractional photothermolysis, only a portion of the overall target tissue is directly treated, which allows a higher level of treatment in those small areas than would be desired with a broad area treatment. The level of treatment can be adjusted by adjusting the treatment density of treatment within the irradiated area. Treating fractionally allows the light energy to be increased to the point where tissue treatment occurs routinely without causing slow healing and other side effects. Fractional photothermolysis thus accomplishes more reproducible treatment in the treated areas by sparing healthy tissue in the regions between treatment zones.
To improve the uniformity of treatment and to reduce the visibility of the treatment zones when used to treat skin for cosmetic procedures, the treatment zones for fractional phototherapy are typically limited to 50-300 μm in diameter and final treatment densities of 500-3000 treatment zones per cm2 are typically used. To treat large areas at these high densities at commercially viable speeds, a fast scanning system or an array of microlenses may be used. Both of these systems are expensive and can be subject to precise alignment tolerances. In addition, these systems can be painful. In addition, moving parts in the scanning system can wear out, thus reducing reliability.
One limitation of fractional resurfacing technology is that the dermal-epidermal junction (DE junction) is the weakest portion of the skin. High density fractional treatments can lead to separation of the DE junction, which can slow the healing process. Very high density fractional treatments can approach broad area treatment and can suffer from similar side effects. However, using higher density of dermal treatment while limiting treatment coverage at the DE junction is desired for some cosmetic treatments, such as the treatment of wrinkles.
Therefore, there is a need for phototherapy approaches that spare healthy tissue surrounding treatment zones to permit rapid healing with low side effects, avoid the use of complex optical systems and moving parts, reduce the pain associated with fractional laser treatments, and/or reduce limitations on dermal treatment density.